U.S. patent number 9,949,507 [Application Number 14/354,349] was granted by the patent office on 2018-04-24 for aerosol generating system with improved aerosol production.
This patent grant is currently assigned to Philip Morris Products S.A.. The grantee listed for this patent is Philip Morris Products S.A.. Invention is credited to Jean-Marc Flick.
United States Patent |
9,949,507 |
Flick |
April 24, 2018 |
Aerosol generating system with improved aerosol production
Abstract
There is provided a method of controlling aerosol production in
an aerosol-generating device, the device including an
aerosol-forming substrate, a heater including at least one heating
element for heating the aerosol-forming substrate, and a power
source for providing power to the heating element, the method
including determining the temperature of the heating element; and
adjusting the power to the heating element to maintain the
temperature of the heating element within a desired temperature
range, wherein the desired temperature range is dynamically
calculated based on a measured flow rate of gas through or past the
device. By controlling the temperature of the heating element, an
aerosol with consistent and desirable properties can be
produced.
Inventors: |
Flick; Jean-Marc (Pomy,
CH) |
Applicant: |
Name |
City |
State |
Country |
Type |
Philip Morris Products S.A. |
Neuchatel |
N/A |
CH |
|
|
Assignee: |
Philip Morris Products S.A.
(Neuchatel, CH)
|
Family
ID: |
47226115 |
Appl.
No.: |
14/354,349 |
Filed: |
October 25, 2012 |
PCT
Filed: |
October 25, 2012 |
PCT No.: |
PCT/EP2012/071165 |
371(c)(1),(2),(4) Date: |
April 25, 2014 |
PCT
Pub. No.: |
WO2013/060781 |
PCT
Pub. Date: |
May 02, 2013 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20140299141 A1 |
Oct 9, 2014 |
|
Foreign Application Priority Data
|
|
|
|
|
Oct 27, 2011 [EP] |
|
|
11250875 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A24F
40/50 (20200101); H05B 1/0202 (20130101); A24F
40/10 (20200101) |
Current International
Class: |
A24F
47/00 (20060101); H05B 1/02 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1210020 |
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Mar 1999 |
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CN |
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102014677 |
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Apr 2011 |
|
CN |
|
2 110 033 |
|
Oct 2009 |
|
EP |
|
2 113 178 |
|
Nov 2009 |
|
EP |
|
2001-502542 |
|
Feb 2001 |
|
JP |
|
2005-034021 |
|
Feb 2005 |
|
JP |
|
2006-524494 |
|
Nov 2006 |
|
JP |
|
2010-506594 |
|
Mar 2010 |
|
JP |
|
2011-515093 |
|
May 2011 |
|
JP |
|
72 821 |
|
May 2008 |
|
RU |
|
WO 2006/028843 |
|
Mar 2006 |
|
WO |
|
WO 2009/132793 |
|
Nov 2009 |
|
WO |
|
Other References
Office Action dated Sep. 30, 2015 in Chinese Patent Application No.
201280052497.0 (submitting English translation only). cited by
applicant .
Office Action dated Aug. 8, 2016 in Japanese Patent Application No.
2014-537615 (submitting English translation only). cited by
applicant .
Office Action dated Aug. 8, 2016 in Taiwanese Patent Application
No. 101139462 (submitting English translation only). cited by
applicant .
Office Action dated Aug. 11, 2016 in GCC Patent Application No. GC
2012-22826 (submitting English translation only). cited by
applicant .
International Search Report dated Feb. 27, 2013, in
PCT/EP12/071165, filed Oct. 25, 2012. cited by applicant .
Written Opinion of the International Searching Authority dated Apr.
2005 in PCT/EP12/071165 filed Oct. 25, 2012. cited by applicant
.
Russian Federation Office Action dated Dec. 15, 2016 in Patent
Application No. 2014121213/12(034178) (submitting English
translation only). cited by applicant .
Extended European Search Report dated Mar. 23, 2012 in Patent
Application No. 11250875.9. cited by applicant .
International Preliminary Report on Patentability and Written
Opinion dated Apr. 29, 2014 in PCT/EP2012/071165. cited by
applicant .
Office Action dated Jun. 2, 2017 in Chinese Patent Application No.
201260052497.0 (submitting English translation only). cited by
applicant.
|
Primary Examiner: Felton; Michael J
Attorney, Agent or Firm: Oblon, McClelland, Maier &
Neustadt, L.L.P.
Claims
The invention claimed is:
1. A method of controlling aerosol production in an electrically
heated device, the device comprising: a heater comprising at least
one heating element; and a power source for providing power to the
at least one heating element, the method comprising the steps of:
determining a temperature of the at least one heating element; and
adjusting the power to the at least one heating element to maintain
the temperature of the at least one heating element within a
desired temperature range, wherein the desired temperature range is
dynamically calculated based on a measured flow rate of gas through
or past the device.
2. The method according to claim 1, wherein the desired temperature
range is dependent on a composition of an aerosol-forming substrate
received in the device.
3. The method according to claim 1, further comprising providing an
initial power to the at least one heating element, wherein the step
of adjusting the power to the t least one heating element is
performed only when the heating element has reached a specific
temperature within the desired temperature range.
4. The method according to claim 1, wherein the step of adjusting
the power is performed only after specific time has elapsed
following detection of a flow of gas through the device exceeding a
predetermined threshold flow rate.
5. The method according to claim 1, further comprising the step of
cutting or reducing power to the heating element based on a
calculated parameter related to flow rate following the step of
adjusting.
6. The method according to claim 1 wherein the step of adjusting
the power to the heating element comprises adjusting a frequency or
a pulse width modulation of a pulsed power signal.
7. The method according to claim 1, wherein the desired temperature
range consists of a single desired temperature.
Description
CROSS REFERENCE TO RELATED APPLICATION
This application is a national phase application based on
PCT/EP2012/071165, filed on Oct. 25, 2012.
The present invention relates to a method for controlling aerosol
production. The present invention further relates to an aerosol
generating system and more specifically to an electrically operated
aerosol generation system. The present invention finds particular
application as a method for controlling aerosol production in an
aerosol generation system through at least one electric element of
an electrically operated smoking system.
WO-A-2009/132793 discloses an electrically heated smoking system. A
liquid is stored in a liquid storage portion, and a capillary wick
has a first end which extends into the liquid storage portion for
contact with the liquid therein, and a second end which extends out
of the liquid storage portion. A heating element heats the second
end of the capillary wick. The heating element is in the form of a
spirally wound electric heating element in electrical connection
with a power supply, and surrounding the second end of the
capillary wick. In use, the heating element may be activated by the
user to switch on the power supply. Suction on a mouthpiece by the
user causes air to be drawn into the electrically heated smoking
system over the capillary wick and heating element and subsequently
into the mouth of the user.
It is an objective of the present invention to provide an improved
method of controlling the amount of power provided to the electric
heating element of such an electrically heated aerosol generating
system.
One particular difficulty with an aerosol generating device is
generating an aerosol with consistent properties in spite of
variations in the flow rate through the device. For example, in a
device in which air flow rate is generated by user inhalations,
variations in the flow rate through the device can occur during the
course of a single inhalation by a user or from one inhalation to
the next.
It would be beneficial to generate an aerosol with the same droplet
size and density, on a consistent basis, regardless of variations
in air flow rate of a gas, such as air, through the device.
According to one aspect of the invention, there is provided a
method of controlling aerosol production in an aerosol-generating
device, the device comprising:
a heater comprising at least one heating element; and
a power source for providing power to the heating element,
comprising the steps of:
determining the temperature of the heating element; and
adjusting the power to the heating element to maintain the
temperature of the heating element within a desired temperature
range, wherein the desired temperature range is dynamically
calculated based on a measured flow rate of gas through or past the
device.
Preferably, the device is configured to allow the air flow to be
generated by a user inhalation. The device may also be an
electrically heated smoking system.
An aerosol is a suspension of solid particles or liquid droplets in
a gas, such as air. When aerosol is produced using a heating
element to vaporise a substrate, the rate of aerosol production and
the properties of the produced aerosol are dependent on the
temperature of the heating element. The temperature of the heating
element is determined not only by the power supplied to the heating
element but also by environmental factors. In particular, the flow
rate of gases past a heating element has a significant cooling
affect on the heating element.
One example of a system in which there are variations in air flow
rate is a system in which the air flow is generated by a user
inhalation, such as an electrically operated smoking system. The
variations in flow rate through the device can occur during the
course of a single inhalation by a user and from one inhalation to
the next. Different users have different inhalation behaviour, and
a single user can have different inhalation behaviours at different
times. The difference in inhalation behaviour could occur during a
single inhalation, but also from inhalation to inhalation. So it is
desirable to have a control method that compensates for different
user and inhalation behaviours.
The desired temperature range of the heating element may consist of
a single desired temperature. Alternatively, the temperature range
of the heating element may span, for example, tens of degrees
Celcius. The acceptable range of temperatures is those temperatures
that allow an aerosol with the desired properties to be formed. If
the temperature is too high there may be undesirable chemicals
formed in the aerosol, if the temperature is too low the substrate
may not be sufficiently vaporised and the droplet size within the
aerosol may be too large.
The desired temperature range may be dependent on a composition of
the aerosol-forming substrate. Different substrates will have
different enthalpy of vaporisation and will suffer from chemical
breakdown at different temperatures. Accordingly, the method may
further comprise the step of determining a characteristic or
identity of the aerosol-forming substrate and calculating or
selecting the desired temperature range based on the characteristic
or identity. For example, the step of determining a characteristic
of the aerosol-forming substrate may comprise reading an indication
of the identity of the aerosol-forming substrate formed in, or on a
housing of, the aerosol-forming substrate. Once the identity of the
substrate has been determined, the desired temperature range may
then be selected from a database of temperature ranges for
particular identities of aerosol-forming substrate. The indication
of the identity of the aerosol-forming substrate may be, for
example: a barcode or other surface indication; a characteristic of
a substrate housing, such as shape or size; or may be a
characteristic resistance or electrical response associated with a
substrate housing.
In an electrically operated smoking system, for example, for users
that take long but slow inhalations it may be desirable to have a
lower heating element temperature, producing aerosol at a lower
rate. This mimics to some extent the behaviour of a conventional
lit-end combustible cigarette. However, the temperature of the
heating element is maintained above a lower threshold level in
order to ensure an aerosol with desirable properties is formed.
This adjustment of the heater temperature based on flow rate of gas
through or past the device can be used together with stored
temperature ranges for specific substrate compositions. So
adjustment of temperature based on flow rate can be made within a
temperature range set by substrate composition.
Preferably, the step of adjusting the power is performed only after
the heating element has reached a specific temperature within a
desired temperature range. For example, the step of adjusting may
start only after the temperature of the heating element has reached
a mid-point of the predetermined temperature range.
Alternatively, or in addition, the step of adjusting the power may
be performed only after a specific time has elapsed following
detection of a flow of gas through the device that exceeds a
predetermined threshold flow rate. It is desirable to heat the
heating element as quickly as possible, given an available power
supply. This is so that the aerosol with the desired properties is
produced as soon as possible. So a maximum power may be delivered
for a specific time following detection of the start of a user
inhalation.
The method preferably also includes the step of cutting or reducing
power to the heating element following the step of adjusting the
power to maintain the temperature of the heating element. This may
be done based on a predetermined time after activation of the
heating element, a detected flow rate, or a calculated parameter
related to flow rate. This ensures that aerosol production is
stopped when a user inhalation ends.
The step of adjusting the power may comprise adjusting a frequency
or a pulse width modulation of a pulsed power signal. If power is
supplied to the heating element as a pulsed signal, adjusting the
frequency of the pulses or the duty cycle of the pulses is an
effective way to maintain the temperature of the heating element
with a desired range.
The step of determining the temperature of the heating element may
comprise determining an electrical resistance of the heating
element. This provides a convenient and accurate indication of the
temperature. Alternatively, a separate temperature sensor may be
used.
According to another aspect of the invention, there is provided an
electrically operated aerosol generating device, the device
comprising: at least one heating element for forming an aerosol
from a substrate; a power supply for supplying power to the heating
element; and electric circuitry for controlling supply of power
from the power supply to the at least one aerosol generating
element, wherein the electric circuitry is arranged to:
determine the temperature of the heating element and adjust the
power to the heating element to maintain the temperature of the
heating element within a desired temperature range, wherein the
desired temperature range is dynamically calculated based on a
measured flow rate of gas through or past the device.
Preferably, the device is configured to allow the air flow to be
generated by a user inhalation.
The desired temperature range may consist of a single desired
temperature.
The device may be configured to receive an aerosol-forming
substrate. The desired temperature range may be dependent on a
composition of the aerosol-forming substrate. Different substrates
will have different vaporisation temperatures and will suffer from
chemical breakdown at different temperatures. Accordingly, the
device may further comprise means for determining a characteristic
or identity of the aerosol-forming substrate and calculating or
selecting the desired temperature range based on the characteristic
or identity. For example, the device may comprise means for reading
an indication of the identity of the aerosol-forming substrate
formed in or on a housing of the aerosol-forming substrate, and the
desired temperature range may then be selected from a database of
temperature ranges based on the identity of the aerosol-forming
substrate. The indication of the identity of the aerosol-forming
substrate may be, for example, a barcode or other surface
indication, a characteristic of a substrate housing, such as shape
or size, or a characteristic resistance or electrical response
associated with a substrate housing.
The electrical circuitry may be configured to determine the
temperature of the heating element based on a determination of an
electrical resistance of the heating element. Alternatively, the
device may include a separate temperature sensor.
The electric circuitry may comprise a microcontroller. The
microcontroller may include a PID regulator for controlling the
power supplied to the heating element.
Preferably, the electric circuitry is arranged to perform the
method steps of the other aspects of the invention. To perform the
method steps of the other aspects of the invention, the electric
circuitry may be hardwired. More preferably, however, the electric
circuitry is programmable to perform the method steps of the other
aspects of the invention.
The heater may comprise a single heating element. Alternatively, it
may be an electrical heater comprising one heating element.
Alternatively, the electric heater may comprise more than one
heating element, for example two, or three, or four, or five, or
six or more heating elements. Alternatively, the electrical heater
may comprise at least one heating element for heating the
substrate. The heating element or heating elements may be arranged
appropriately so as to most effectively heat the aerosol-forming
substrate.
The at least one electric heating element preferably comprises an
electrically resistive material. Suitable electrically resistive
materials include but are not limited to: semiconductors such as
doped ceramics, electrically "conductive" ceramics (such as, for
example, molybdenum disilicide), carbon, graphite, metals, metal
alloys and composite materials made of a ceramic material and a
metallic material. Such composite materials may comprise doped or
undoped ceramics. Examples of suitable doped ceramics include doped
silicon carbides. Examples of suitable metals include titanium,
zirconium, tantalum and metals from the platinum group. Examples of
suitable metal alloys include stainless steel, Constantan, nickel-,
cobalt-, chromium-, aluminium-titanium-zirconium-, hafnium-,
niobium-, molybdenum-, tantalum-, tungsten-, tin-, gallium-,
manganese- and iron-containing alloys, and super-alloys based on
nickel, iron, cobalt, stainless steel, Timetal.RTM., iron-aluminium
based alloys and iron-manganese-aluminium based alloys.
Timetal.RTM. is a registered trade mark of Titanium Metals
Corporation, 1999 Broadway Suite 4300, Denver Colo. In composite
materials, the electrically resistive material may optionally be
embedded in, encapsulated or coated with an insulating material or
vice-versa, depending on the kinetics of energy transfer and the
external physicochemical properties required. The heating element
may comprise a metallic etched foil insulated between two layers of
an inert material. In that case, the inert material may comprise
Kapton.RTM., all-polyimide or mica foil. Kapton.RTM. is a
registered trade mark of E.I. du Pont de Nemours and Company, 1007
Market Street, Wilmington, Del. 19898, United States of
America.
Alternatively, the at least one electric heating element may
comprise an infra-red heating element, a photonic source, or an
inductive heating element.
The at least one electric heating element may take any suitable
form. For example, the at least one electric heating element may
take the form of a heating blade. Alternatively, the at least one
electric heating element may take the form of a casing or substrate
having different electro-conductive portions, or an electrically
resistive metallic tube. If the aerosol-forming substrate is a
liquid provided within a container, the container may incorporate a
disposable heating element. Alternatively, one or more heating
needles or rods that run through the centre of the aerosol-forming
substrate may also be suitable. Alternatively, the at least one
electric heating element may be a disk (end) heating element or a
combination of a disk heating element with heating needles or rods.
Alternatively, the at least one electric heating element may
comprise a flexible sheet of material arranged to surround or
partially surround the aerosol-forming substrate. Other
alternatives include a heating wire or filament, for example a
Ni--Cr, platinum, tungsten or alloy wire, or a heating plate.
Optionally, the heating element may be deposited in or on a rigid
carrier material.
The at least one electric heating element may comprise a heat sink,
or heat reservoir comprising a material capable of absorbing and
storing heat and subsequently releasing the heat over time to the
aerosol-forming substrate. The heat sink may be formed of any
suitable material, such as a suitable metal or ceramic material.
Preferably, the material has a high heat capacity (sensible heat
storage material), or is a material capable of absorbing and
subsequently releasing heat via a reversible process, such as a
high temperature phase change. Suitable sensible heat storage
materials include silica gel, alumina, carbon, glass mat, glass
fibre, minerals, a metal or alloy such as aluminium, silver or
lead, and a cellulose material such as paper. Other suitable
materials which release heat via a reversible phase change include
paraffin, sodium acetate, naphthalene, wax, polyethylene oxide, a
metal, metal salt, a mixture of eutectic salts or an alloy.
The heat sink or heat reservoir may be arranged such that it is
directly in contact with the aerosol-forming substrate and can
transfer the stored heat directly to the substrate. Alternatively,
the heat stored in the heat sink or heat reservoir may be
transferred to the aerosol-forming substrate by means of a heat
conductor, such as a metallic tube.
The at least one heating element may heat the aerosol-forming
substrate by means of conduction. The heating element may be at
least partially in contact with the substrate, or the carrier on
which the substrate is deposited. Alternatively, the heat from the
heating element may be conducted to the substrate by means of a
heat conductive element.
Alternatively, the at least one heating element may transfer heat
to the incoming ambient air that is drawn through the electrically
heated aerosol generating device during use, which in turn heats
the aerosol-forming substrate by convection. The ambient air may be
heated before passing through the aerosol-forming substrate.
Alternatively, if the aerosol-forming substrate is a liquid
substrate, the ambient air may be first drawn through the substrate
and then heated.
The aerosol-forming substrate may be a solid aerosol-forming
substrate. The aerosol-forming substrate preferably comprises a
tobacco-containing material containing volatile tobacco flavour
compounds which are released from the substrate upon heating. The
aerosol-forming substrate may comprise a non-tobacco material. The
aerosol-forming substrate may comprise tobacco-containing material
and non-tobacco containing material. Preferably, the
aerosol-forming substrate further comprises an aerosol former.
Examples of suitable aerosol formers are glycerine and propylene
glycol.
Alternatively, the aerosol-forming substrate may be a liquid
aerosol-forming substrate. In one embodiment, the electrically
heated aerosol generating device further comprises a liquid storage
portion. Preferably, the liquid aerosol-forming substrate is stored
in the liquid storage portion. In one embodiment, the electrically
heated aerosol generating device further comprises a capillary wick
in communication with the liquid storage portion. It is also
possible for a capillary wick for holding liquid to be provided
without a liquid storage portion. In that embodiment, the capillary
wick may be preloaded with liquid.
Preferably, the capillary wick is arranged to be in contact with
liquid in the liquid storage portion. In that case, in use, liquid
is transferred from the liquid storage portion towards the at least
one electric heating element by capillary action in the capillary
wick. In one embodiment, the capillary wick has a first end and a
second end, the first end extending into the liquid storage portion
for contact with liquid therein and the at least one electric
heating element being arranged to heat liquid in the second end.
When the heating element is activated, the liquid at the second end
of the capillary wick is vaporized by the heating element to form
the supersaturated vapour. The supersaturated vapour is mixed with
and carried in the airflow. During the flow, the vapour condenses
to form the aerosol and the aerosol is carried towards the mouth of
a user. The heating element in combination with a capillary wick
may provide a fast response, because that arrangement may provide a
high surface area of liquid to the heating element. Control of the
heating element according to the invention may therefore depend on
the structure of the capillary wick arrangement.
The liquid substrate may be absorbed into a porous carrier
material, which may be made from any suitable absorbent plug or
body, for example, a foamed metal or plastics material,
polypropylene, terylene, nylon fibres or ceramic. The liquid
substrate may be retained in the porous carrier material prior to
use of the electrically heated aerosol generating device or
alternatively, the liquid substrate material may be released into
the porous carrier material during, or immediately prior to use.
For example, the liquid substrate may be provided in a capsule. The
shell of the capsule preferably melts upon heating and releases the
liquid substrate into the porous carrier material. The capsule may
optionally contain a solid in combination with the liquid.
If the aerosol-forming substrate is a liquid substrate, the liquid
has physical properties. These include, for example, a boiling
point, vapour pressure, and surface tension characteristics to make
them suitable for use in the aerosol generating device. Control of
the at least one electric heating element may depend upon the
physical properties of the liquid substrate. The liquid preferably
comprises a tobacco-containing material comprising volatile tobacco
flavour compounds which are released from the liquid upon heating.
Alternatively, or in addition, the liquid may comprise a
non-tobacco material. The liquid may include water, solvents,
ethanol, plant extracts and natural or artificial flavours.
Preferably, the liquid further comprises an aerosol former.
Examples of suitable aerosol formers are glycerine and propylene
glycol.
An advantage of providing a liquid storage portion is that a high
level of hygiene can be maintained. Using a capillary wick
extending between the liquid and the electric heating element,
allows the structure of the device to be relatively simple. The
liquid has physical properties, including viscosity and surface
tension, which allow the liquid to be transported through the
capillary wick by capillary action. The liquid storage portion is
preferably a container. The liquid storage portion may not be
refillable. Thus, when the liquid in the liquid storage portion has
been used up, the aerosol generating device is replaced.
Alternatively, the liquid storage portion may be refillable. In
that case, the aerosol generating device may be replaced after a
certain number of refills of the liquid storage portion.
Preferably, the liquid storage portion is arranged to hold liquid
for a pre-determined number of puffs.
The capillary wick may have a fibrous or spongy structure. The
capillary wick preferably comprises a bundle of capillaries. For
example, the capillary wick may comprise a plurality of fibres or
threads, or other fine bore tubes. The fibres or threads may be
generally aligned in the longitudinal direction of the aerosol
generating device. Alternatively, the capillary wick may comprise
sponge-like or foam-like material formed into a rod shape. The rod
shape may extend along the longitudinal direction of the aerosol
generating device. The structure of the wick forms a plurality of
small bores or tubes, through which the liquid can be transported
to the electric heating element, by capillary action. The capillary
wick may comprise any suitable material or combination of
materials. Examples of suitable materials are ceramic- or
graphite-based materials in the form of fibres or sintered powders.
The capillary wick may have any suitable capillarity and porosity
so as to be used with different liquid physical properties such as
density, viscosity, surface tension and vapour pressure. The
capillary properties of the wick, combined with the properties of
the liquid, ensure that the wick is always wet in the heating
area.
The aerosol-forming substrate may alternatively be any other sort
of substrate, for example, a gas substrate, or any combination of
the various types of substrate. During operation, the substrate may
be completely contained within the electrically heated aerosol
generating device. In that case, a user may puff on a mouthpiece of
the electrically heated aerosol generating device. Alternatively,
during operation, the substrate may be partially contained within
the electrically heated aerosol generating device. In that case,
the substrate may form part of a separate article and the user may
puff directly on the separate article.
The device may include a flow sensor for detecting a flow rate of
gas through the device. The sensor may be any sensor which can
detect airflow, such as airflow indicative of a user inhaling. The
sensor may be an electro-mechanical device. Alternatively, the
sensor may be any of: a mechanical device, an optical device, an
opto-mechanical device, a micro electro mechanical devices (MEMS)
based sensor and an acoustic sensor. The sensor can be a thermal
conductive flow sensor, a pressure sensor, an anemometer and should
be able to not only detect an airflow but should be able to measure
the airflow. So, the sensor should be able to deliver an analogue
electrical signal or digital information that is representative of
the amplitude of the air flow.
The electrically heated aerosol generating device may comprise an
aerosol-forming chamber in which aerosol forms from a super
saturated vapour, which aerosol is then carried into the mouth of a
user. An air inlet, air outlet and the chamber are preferably
arranged so as to define an airflow route from the air inlet to the
air outlet via the aerosol-forming chamber, so as to convey the
aerosol to the air outlet and into the mouth of a user.
Preferably, the aerosol generating device comprises a housing.
Preferably, the housing is elongate. The structure of the housing,
including the surface area available for condensation to form, will
affect the aerosol properties and whether there is liquid leakage
from the device. The housing may comprise a shell and a mouthpiece.
In that case, all the components may be contained in either the
shell or the mouthpiece. The housing may comprise any suitable
material or combination of materials. Examples of suitable
materials include metals, alloys, plastics or composite materials
containing one or more of those materials, or thermoplastics that
are suitable for food or pharmaceutical applications, for example
polypropylene, polyetheretherketone (PEEK) and polyethylene.
Preferably, the material is light and non-brittle. The material of
the housing may affect the amount of condensation forming on the
housing which will, in turn, affect liquid leakage from the
device
Preferably, the aerosol generating device is portable. The aerosol
generating device may be a smoking device and may have a size
comparable to a conventional cigar or cigarette. The smoking device
may have a total length between approximately 30 mm and
approximately 150 mm. The smoking device may have an external
diameter between approximately 5 mm and approximately 30 mm.
The method and electrically heated aerosol generating device
according to the present invention provide the advantage that the
temperature of the heating element is controlled, thereby providing
a consistent and desirable experience for the user, without
requiring any additional user or device actions.
According to another aspect of the invention, there is provided
electric circuitry for an electrically operated aerosol generating
system, the electric circuitry being arranged to perform the method
of the other aspects of the invention.
Preferably, the electric circuitry is programmable to perform the
method of the other aspects of the invention. Alternatively, the
electric circuitry may be hardwired to perform the method of the
other aspects of the invention.
According to another aspect of the invention, there is provided a
computer program which, when run on programmable electric circuitry
for an electrically operated aerosol generating system, causes the
programmable electric circuitry to perform the method of the other
aspects of the invention.
According another aspect of the invention, there is provided a
computer readable storage medium having stored thereon a computer
program according to the previous aspect of the invention.
Features described in relation to one aspect of the invention may
be applicable to another aspect of the invention.
The invention will be further described, by way of example only,
with reference to the accompanying drawings, in which:
FIG. 1 shows one example of an electrically heated aerosol
generating system in accordance with an embodiment of the
invention;
FIG. 2 illustrates a typical heating element temperature profile
and a typical flow rate profile in a system of the type shown in
FIG. 1;
FIG. 3 illustrates a method of adjusting the power supplied to the
heating element during the puff illustrated in FIG. 2;
FIG. 4 illustrates electric circuitry for controlling the
temperature of the heating element in accordance with the first
embodiment of the invention; and
FIG. 5 illustrates a technique for determining the temperature of
an electrical heating element by measuring electrical
resistance.
FIG. 1 shows one example of an electrically heated aerosol
generating system. In FIG. 1, the system is a smoking system having
a liquid storage portion. The smoking system 100 of FIG. 1
comprises a housing 101 having a mouthpiece end 103 and a body end
105. In the body end, there is provided an electric power supply in
the form of battery 107, electric circuitry in the form of hardware
109 and a puff detection system 111. In the mouthpiece end, there
is provided a liquid storage portion in the form of cartridge 113
containing liquid 115, a capillary wick 117 and a heater 119
comprising at least one heating element. Note that the heating
element is only shown schematically in FIG. 1. One end of the
capillary wick 117 extends into the cartridge 113 and the other end
of the capillary wick 117 is surrounded by the heating element 119.
The heating element is connected to the electric circuitry via
connections 121. The housing 101 also includes an air inlet 123, an
air outlet 125 at the mouthpiece end and an aerosol-forming chamber
127.
In use, operation is as follows. Liquid 115 is transferred or
conveyed by capillary action from the cartridge 113 from the end of
the wick 117 which extends into the cartridge to the other end of
the wick 117 which is surrounded by the heating element 119. When a
user draws on the device at the air outlet 125, ambient air is
drawn through air inlet 123. In the arrangement shown in FIG. 1,
the puff detection system 111 senses the puff and activates the
heating element 119. The battery 107 supplies energy to the heating
element 119 to heat the end of the wick 117 surrounded by the
heating element. The liquid in that end of the wick 117 is
vaporized by the heating element 119 to create a supersaturated
vapour. At the same time, the liquid being vaporized is replaced by
further liquid moving along the wick 117 by capillary action. (This
is sometimes referred to as "pumping action".) The supersaturated
vapour created is mixed with and carried in the airflow from the
air inlet 123. In the aerosol-forming chamber 127, the vapour
condenses to form an inhalable aerosol, which is carried towards
the outlet 125 and into the mouth of the user.
The capillary wick can be made from a variety of porous or
capillary materials and preferably has a known, pre-defined
capillarity. Examples include ceramic- or graphite-based materials
in the form of fibres or sintered powders. Wicks of different
porosities can be used to accommodate different liquid physical
properties such as density, viscosity, surface tension and vapour
pressure. The wick must be suitable so that the required amount of
liquid can be delivered to the heating element. The wick and
heating element must be suitable so that the required amount of
aerosol can be conveyed to the user.
In the embodiment shown in FIG. 1, the hardware 109 and the puff
detection system 111 are preferably programmable. The hardware 109
and puff detection system 111 can be used to manage the device
operation. This assists with control of the particle size in the
aerosol.
FIG. 1 shows one example of an electrically heated aerosol
generating system which may be used with the present invention.
Many other examples are usable with the invention, however. The
electrically heated aerosol generating system simply needs to
include or receive an aerosol forming substrate which can be heated
by at least one electric heating element, powered by a power supply
under the control of electric circuitry. For example, the system
need not be a smoking system. For example, the aerosol forming
substrate may be a solid substrate, rather than a liquid substrate.
Alternatively, the aerosol forming substrate may be another form of
substrate such as a gas substrate. The heating element may take any
appropriate form. The overall shape and size of the housing could
be altered and the housing could comprise a separable shell and
mouthpiece. Other variations are, of course, possible.
As already mentioned, preferably, the electric circuitry,
comprising hardware 109 and the puff detection system 111, is
programmable in order to control the supply of power to the heating
element. This, in turn, controls the temperature profile which
affects the amount and the density of the aerosol produced. The
term "temperature profile" refers to a graphic representation of
the temperature of the heating element (or another similar measure,
for example, the heat generated by the heating element) over the
time taken for a puff, as shown in FIG. 2. Alternatively, the
hardware 109 and the puff detection system 111 may be hardwired to
control the supply of power to the heating element. Again, this
controls the temperature profile which affects the amount and
density of the aerosol generated.
The line 200 in FIG. 2 is a plot of the flow rate of air through
the system during the course of a user puff. The puff lasts around
2 seconds and the flow rate rises from zero to a maximum flow rate
at around 1 second, before dropping back to zero again. This is a
typical puff profile but it should be clear that there can be great
variation from puff to puff and from user to user both in the
maximum flow rate and in the evolution of the flow rate during a
puff.
The line 210 in Figure is the temperature of the heating element
during the user puff. The temperature profile 210 is divided into
three stages: an initial stage 215, during which maximum power is
applied to the heating element in order to rapidly raise its
temperature; a regulated stage 215, during which the temperature of
the heating element is held constant (or at least within an
acceptable temperature band), and an end of puff stage 220, during
which power to the heater is cut or reduced.
FIG. 3 illustrates the power applied to the heating element during
the user puff shown in FIG. 2. Power is supplied to the heating
element in the form of a pulsed signal 300. In order to regulate
the temperature of the heating element, the pulsed signal is
modulated. As shown in FIG. 3, the average power that is applied to
the heating element can be varied by changing the frequency (or
"PFM"--pulse frequency modulation) of the modulations of the power
signal at fixed duty cycle to keep constant the temperature of the
heating element.
The other way of altering the power applied is PWM (pulse width
modulation), which consists of varying the duty cycle at constant
frequency. The duty cycle is the ratio of the time that the power
is switched on to the time the power is switched off. In other
words, the ratio of the width of the voltage pulses to the time
between the voltage pulses. A low duty cycle of 5% will provide
much less power than a duty cycle of 95%.
As shown in FIG. 3, during the initial stage 215, the power pulses
300 are delivered at high frequency in order to reach the desired
temperature quickly. When the desired temperature is reached the
regulated stage 220 begins. There is a small local maximum just as
the regulated stage begins. This is due to the nature of the PID
control scheme used to regulate the temperature. There is a small
delay between sensing that the desired temperature has been reached
and modulation of the power signal, which gives rise to the local
maximum.
The desired temperature is dynamically calculated depending on the
flow rate of gas past the heating element. For lower flow rates it
is desirable to have a lower temperature. For example, the desired
temperature may be set based on flow rate measured at a fixed time
after activation of the heating element, may be based on an average
flow rate calculated over previous heating cycles, or may be based
on a cumulative flow rate over a fixed period after activation of
the heating element.
In the regulated phase 220 the power pulses are delivered to the
heating element just frequently enough to maintain the desired
temperature. This means that the pulses are delivered at a lower
frequency that during the initial stage. However, as the air flow
rate continues to rise towards its maximum the cooling effect of
the air also increases. This means that the frequency of the power
pulses increases until the maximum flow rate is reached, before
decreasing again as flow rate drops.
In the end of puff stage 220 the power is cut completely. A
decision is taken to cut power before the end of the puff in order
to ensure that all of the generated aerosol is flushed out of the
system by the last portion of the puff. The temperature thus falls
during this period as does aerosol production. The point at which
power is cut or reduced, starting the end of puff stage, can be
based, for example, on a simple time from activation, on a sensed
flow rate or on a more sophisticated calculation that takes into
account the puff profile.
FIG. 4 illustrates the control circuitry used to provide the
described temperature regulation in accordance with one embodiment
of the invention. The system has two parts: a consumable cartridge
113 containing liquid substrate 115, a capillary wick 117 and a
heater 119; and a device part containing, a battery and electric
circuitry 109, as described with reference to FIG. 1. In FIG. 3
only the electric circuit elements are illustrated.
The electrical power is delivered to the heating element 119 from
the battery connection 405, through the measurement resistance R1
and the transistor T1. The frequency modulation of the PWM power
signal is controlled by the microcontroller 420 and delivered via
its analog output 425 to the transistor T1 which acts as a simple
switch.
The regulation is based on a PID regulator that is part of the
software integrated in the microcontroller 420. The temperature (or
an indication of the temperature) of the heating element is
determined by measuring the electrical resistance of the heating
element.
The analog input 430 on the microcontroller 420 is used to collect
the voltage across the resistance R1 and provides the image of the
electrical current flowing in the heating element. The battery
voltage V+ and the voltage across R1 are used to calculate the
heating element resistance variation and or its temperature, as
described with reference to FIG. 5.
The resistance R3 in the consumable part is used to identify the
substrate composition. The resistances R3 and R2 are a simple
voltage divider from which the voltage level is collected by the
microcontroller 420 via its analog input 435 by activating
transistor T2. The voltage converted will then be proportional to
the resistance R3. A look-up table of resistance values for R3 and
corresponding temperature ranges or resistance ranges for the
heating element is located in an address memory in the
microcontroller and is used to set the PID regulator and the
temperature level at which the heating element will operate.
FIG. 5 is a schematic electric circuit diagram showing how the
heating element resistance may be measured in the system of the
type shown in FIG. 4. In FIG. 5, the heater 501 is connected to a
battery 503 which provides a voltage V2. The heater resistance to
be measured at a particular temperature is R.sub.heater. In series
with the heater 501, an additional resistor 505, corresponding to
R1 in FIG. 4, with known resistance r is inserted connected to
voltage V1, intermediate between ground and voltage V2. In order
for microprocessor 507 to measure the resistance R.sub.heater of
the heater 501, the current through the heater 501 and the voltage
across the heater 501 can both be determined. Then, the following
well-known formula can be used to determine the resistance: V=IR
(1)
In FIG. 5, the voltage across the heater is V2-V1 and the current
through the heater is I. Thus:
.times..times..times..times. ##EQU00001##
The additional resistor 505, whose resistance r is known, is used
to determine the current I, again using (1) above. The current
through the resistor 505 is I and the voltage across the resistor
505 is V1. Thus:
.times..times. ##EQU00002##
So, combining (2) and (3) gives:
.times..times..times..times..times..times..times. ##EQU00003##
Thus, the microprocessor 507 can measure V2 and V1, as the aerosol
generating system is being used and, knowing the value of r, can
determine the heater's resistance at a particular temperature,
R.sub.heater.
The following formula can be used to relate the temperature T to
the measured resistance R.sub.heater at temperature T:
##EQU00004## where A is the thermal resistivity coefficient of the
heating element material and R.sub.0 is the resistance of the
heating element at room temperature T.sub.0.
An advantage of this embodiment is that no temperature sensor,
which can be bulky and expensive, is required. Also the resistance
value can be used directly by the PID regulator instead of
temperature. If the resistance value is held within a desired
range, so too will the temperature of the heating element.
Accordingly the actual temperature of the heating element need not
be calculated. However, it is possible to use a separate
temperature sensor and connect that to the microcontroller to
provide the necessary temperature information.
Although the embodiment described comprises a consumable part and a
device part, the invention is applicable to other constructions of
aerosol-generating device. It should also be clear that the
temperature or resistance of the heating element need not be
directly measured. For example, the temperature of the heating
element may be estimated based on other measured parameters, such
as a flow rate through the system, or may be estimated from a
measure of air temperature at a point within the system.
* * * * *